1. Field of the Invention
The present invention relates to an integrated circuit for driving scanning electrodes of a display element of matrix type, such as a LCD (Liquid Crystal Display) element of active matrix type, an EL (Electroluminescence) display element and so on.
2. Description of the Related Arts
Such a display element, which is driven by this kind of driving integrated circuit, can be utilized in a liquid crystal television and other various kinds of display devices.
In the control device of the conventional art, a clock signal of a predetermined cycle is generated and a pulse signal is also generated such that the pulse signal is a high level during one cycle of the clock signal. In this driving integrated circuit, the pulse signal is taken in at the pulse rise timing of the clock signal and is held to become a control signal.
This driving integrated circuit also includes a shift register which takes in the control signal as a serial signal, by use of the clock signal as a shift clock, so as to output a parallel signal. Then, each outputted parallel signal from the shift register is gated with an inverted signal of the clock signal, by use of a NAND gate. Then, the level of thus gated signal is corrected, and thus level-corrected signal is outputted as a driving pulse from the output terminals of the driving integrated circuit.
In this manner, when the control signal is once taken in by the shift register, it is synchronized with the shift clock and is moved across the shift register, so that the driving pulse is correspondingly outputted from each output terminal.
On the other hand, the liquid crystal display element, which is to be driven by this type of driving integrated circuit, is equipped with a plurality of scanning electrodes. Each scanning electrode is sequentially driven by giving the driving pulse from each corresponding output terminal of the driving integrated circuit, such that one whole display surface of the liquid crystal display element is scanned by the scanning electrodes in one operation period, and one display image is formed on the display surface according to the image signal supplied to the signal electrodes arranged in the liquid crystal display element. By repeating this image forming process sequentially, the moving picture can be formed on the liquid crystal display element, so that the liquid crystal television can be realized.
When the liquid crystal panel including the TFT (Thin Film Transistor) is to be driven at a high speed, in order to prevent the degradation of the contrast, it becomes necessary to select and drive each scanning electrode twice or more than twice successively during above-mentioned one operation period.
However, in case of the above explained driving integrated circuit, only one driving pulse can be outputted from one output terminal during one operation period. Accordingly, in order to select and drive one scanning electrode successively twice in one operation period for example, it becomes necessary to have two driving integrated circuits, for outputting two driving pulses with respect to one scanning electrode in one operation period, which timings are different from each other, and to use thus outputted driving pulses in a parallel manner.
However, it is very difficult in a practical sense to install two or more the driving integrated circuits to one liquid crystal display element and to establish such a circuit arrangement and electrical connections to supply the driving signals in the above mentioned parallel manner.